It has been proposed previously to provide a seat-belt pretensioner adapted to apply tension to a seat-belt when an accident situation or a potential accident situation is detected. When the pretensioner operates the occupant of the seat is pulled tightly into the seat before a situation arises in which the occupant moves forwardly relative to the seat. Thus the seat-belt can maintain the occupant of the seat in a position which is as far as possible from the steering wheel or dashboard of the vehicle. Consequently it will be understood that the pretensioner minimises the distance that the occupant of the seat moves forwardly before the seat-belt retards that forward movement.
If a vehicle which is provided with a pretensioner is involved in an accident such as a roll over crash, the pretensioner will be activated and will serve to apply tension to the seat-belt, thus tending to hold the occupant of the seat firmly in position. However, during a roll over crash, the vehicle may impact the ground very severely, with the effect that the occupant of the seat moves downwardly into the seat, against the ordinary spring bias provided in the squab of the seat, or the back of the seat. This can create a xe2x80x9cslackxe2x80x9d in the seat-belt. This is disadvantageous and potentially dangerous. If the occupant of the seat bounces back towards the seat-belt, the occupant, travelling with a predetermined velocity, will engage the seat-belt, which will not yield, and this may injure the occupant of the seat. Also, if the seat belt is effectively xe2x80x9cslackxe2x80x9d, the occupant of the seat may not be retained in position, and may move, relative to the seat.
It is to be appreciated that a slack may also occur in a seat-belt if, as a consequence of deformation of the vehicle, or deformation of the seat, during the roll over situation, the total distance between the anchoring points provided at the ends of the seat-belt becomes reduced.
The present invention seeks to provide a pretensioner which, in use, will reduce or obviate the disadvantages of the prior proposed pretensioners as discussed above.
According to this invention there is provided a pretensioner unit for use in pretensioner a safety-belt, the pretensioner unit incorporating an elongate housing, and a unit for movement along the housing, the unit having, at one end, an end-element associated with means which permit movement of the end-element in a first direction along the housing, but which prevent movement of the end-element in the opposite direction, the said end-element being connected to a compressed resilient means extending between said end-element and a connector element tending to bias the connector element away from the end-element, the said connector element connecting the resilient means to one end of an elongate flexible element, which flexible element is adapted to be connected to part of a safety-belt arrangement, compression maintaining means being provided which block movement of the connector element away from said end-element, thus maintaining compression within the resilient means, the pretensioner incorporating means to apply a force to said end-element to move the end-element in the first direction and to disable the compression maintaining means in response to an accident situation being detected, thus applying tension to the flexible element to draw in the flexible element, the resilient means then applying a biasing force to the connector element adapted to draw the flexible element into the housing should a safety-belt with which the unit is used become slack, there being means to prevent the flexible element from subsequently being paid out after having been drawn in.
Preferably the elongate flexible element comprises a wire or cable connected to a buckle forming part of a safety-belt arrangement.
Advantageously the unit is received within a generally cylindrical chamber within the elongate housing, the means which permit movement of the end-element in the first direction but not in the opposite direction comprising a peripheral groove formed in the end-piece, the groove being of tapering form and containing one or more elements moveable axially of the chamber within the groove.
Conveniently the resilient means comprises a helical compression spring.
Preferably the means to prevent the flexible element from subsequently being paid out after having been drawn in comprise a peripheral groove of tapering form formed on a peripheral wall of the connector element, the groove containing one or more elements engageable between the base of the groove and the wall of a chamber defined by the housing in which the unit is located.
Alternatively the means that prevent the flexible element from subsequently being paid out comprise a rotationally mounted element provided with teeth adapted to compress the flexible element against a plate in response to a tendency of the flexible element to be paid out.
Preferably the means to apply a force to the end-element comprise a gas generator adapted to supply gas to one face of the end-element, the end-element being in the form of a piston.
In one embodiment the compression maintaining means comprise a frangible element engaging said connector element, the frangible element being adapted to be broken when gas from the gas generator applies a predetermined force to the end-element.
In an alternative embodiment the compression maintaining means comprises a rigid elongate member which extends from the end element to the connector element, one end of the elongate member being connected to one said element, the other end of the elongate member passing through a bore in the other said element, the said other end of the elongate element being provided with a resilient catch initially engaging an abutment provided in the bore to prevent the elements moving apart, the compressed resilient means being partially compressed so that when said force is applied to the end element, the elongate member moves relative to the bore to move the resilient catch out of the bore, the resilient catch being adapted to become disengaged from the rigid member on being moved out of the bore.
Preferably the bore defines a main region having a first diameter and a terminal region having a larger diameter, the abutment being defined by the intersection between the main region and the terminal region.
Conveniently the resilient catch comprises a resilient ring compressible from a relatively large diameter to a relatively small diameter the resilient ring being such that, when compressed to the relatively small diameter, the resilient ring engages is retained in a groove formed in the rigid elongate member, the ring being retained in the groove by the side-wall of the bore.
In an alternative embodiment the compression maintaining means are adapted to be disabled in response to movement of a further piston which receives gas from the gas generator.
Conveniently the compression maintaining means comprises a pivotally mounted latch adapted, in one position, to engage and retain the connector element, part of the latch directly or indirectly engaging a stop to prevent the latch rotating to a release position, the stop being moveable by said further piston.
Preferably part of the pivotally mounted latch engages an elongate rod, the elongate rod engaging a stop constituted by a member moved by or formed integrally with said further piston.
Alternatively the further piston acts on one end of an elongate arm which is pivotally mounted for movement relative to the housing, the elongate arm carrying a finger which initially extends into the housing to engage the connector element, the elongate arm being pivotally movable, on actuation of the further piston, to a position in which the finger no longer engages the connector element.
Conveniently two further pistons are provided each connected with an associated said elongate arm.
In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: